JP 2000-338231 A describes an art related to a radar apparatus that detects an intruding object by utilizing a radiowave such as microwave.
Also, JP 2002-236171 A discloses a radar system that detects an intruding object, and determines whether the intruding object is a human body or not, based on the radar cross section calculated from the signal power.
Further, JP 1999-183612 A describes a vehicle-mounted radar system, a signal processing circuit of which determines a distribution of the wave reflection points, and measures the position and width of a target based on the distribution.
Also, JP 2004-239744 A discloses a vehicle-mounted radar system that allows measurement of the width of a detected object.